Space-based communications systems are being designed and deployed by a number of different organizations. Space-based systems provide unique opportunities and problems because of the space environment. One set of the problems is introduced by the antenna requirements. The antenna problem is particularly important to the design of space-based communication systems. In some cases, large antennas have dominated the design of spacecraft. The antenna problem is also important for airborne communications platforms.
Phased array antennas have been used extensively on-board satellites and aircraft. Phased array antennas can lead to lower operational costs and more payload functionality. Reducing the number of antennas has also been examined by a number of different space-based communication system designers.
Using a single main mission antenna (MMA) that can both transmit and receive could greatly simplify the spacecraft design and lower costs. However, when the uplink and downlink frequency bands are close together, it is difficult to isolate the uplinks and downlinks by filtering and a different technique must be employed.
There is a significant need for a method of operating a communications system that mitigates the isolation requirements on space-based communications platforms within the system. In addition, there is a significant need for a method for using a single antenna on a space-based communications platform while maintaining spectral capacity.